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iOSOperating system · Cisco

CVE-1999-0160

HIGH · 7.5 CVSS v2.0 Published 1997-10-01
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Some classic Cisco IOS devices have a vulnerability in the PPP CHAP authentication to establish unauthorized PPP connections.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

Classic Cisco IOS devices contain a vulnerability in the PPP CHAP (Challenge Handshake Authentication Protocol) authentication mechanism that allows attackers to establish unauthorized PPP connections without valid credentials.

MitigationUpgrade affected devices to a patched Cisco IOS version, or if devices are end-of-life, replace them. Implement additional network access controls around PPP endpoints as a compensating control.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
iOSOperating system
Affected:= 4.1= 9.1= 10.3= 11.0= 11.1= 11.2= 11.2p

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Authentication
None
Confidentiality
Partial
Integrity
Partial
Availability
Partial

AV:N/AC:L/Au:N/C:P/I:P/A:P

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify the Cisco IOS version
    Run 'show version' on the device console or via telnet/ssh and locate the 'IOS' line showing the version number (for example, 'IOS (tm) 3000 Software...').
    Affected if The version matches one of the affected releases: 4.1, 9.1, 10.3, 11.0, 11.1, 11.2, or 11.2p.
  2. Check if PPP is enabled on any interface
    Run 'show running-config | include ppp' or 'show interface' and look for interfaces with 'PPP' in the encapsulation type.
    Affected if PPP encapsulation is configured on any interface (for example, 'encapsulation ppp' under a serial or dialer interface).
  3. Verify CHAP authentication is configured for PPP
    Run 'show running-config' and search for 'ppp authentication chap' under the relevant interface configuration, or use 'show ip interface' to see authentication methods.
    Affected if The device has 'ppp authentication chap' or 'ppp authentication chap pap' configured on a PPP interface.
  4. Confirm PPP is accepting incoming connections
    Run 'show ppp interface' or 'show dialer interface' to see active PPP sessions, and check for 'dialer' or 'async' interfaces configured with PPP.
    Affected if The device has PPP interfaces configured to accept incoming calls or dialout connections.

You are affected if your device runs an affected Cisco IOS version (4.1, 9.1, 10.3, 11.0, 11.1, 11.2, or 11.2p) AND has PPP with CHAP authentication enabled and configured to accept connections.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade affected devices to a patched Cisco IOS version, or if devices are end-of-life, replace them. Implement additional network access controls around PPP endpoints as a compensating control.

Fix this in iOS Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-1999-0160 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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